Alloy for bonding metals to ceramics



Ju 1964 J. SCHULTZ, JR

ALLOY FOR BONDING METALS TO CERAMICS Filed March 22, 1962 F'IGJ F'IG.2

H \s ATTORNEY United States Patent 3,137,545 ALLOY FOR BGNDING METALS TCERANICS John Schultz, Jra, Louisville, Ky., assignor to GeneralElectric Company, a corporation of New York Filed Mar. 22, 19:32, Ser.No. 181,539 4 Claims. (Cl. 259-495) The present invention relates to animproved brazing alloy and is more particularly concerned with a fusiblealloy material for directly sealing a metal member to acaramic member.

Various alloys have been used or proposed for making a direct jointbetween a metal member and a ceramic member. In recent years preferredalloys for forming such seals have included small amounts of titanium assuch or in the form the hydride as this metal has been found to providean extremely intimate bond with ceramic surfaces. For example, Patent3,00l,269.Moore et al., describes metal-to-cer amic joint structures inwhich the bonding material is a fusible alloy consisting essentiallyoffrom about 2m 10% by Weight of titanium or zirconium, about 10 to 85%lead and the remainder a metal selected from the group consisting ofcopper, silver and nickel or combinations thereof. While zinc, bismuth,cadmium, indium and tin are described as being possible substitutes forall or part of the lead component of the alloy, the alloys commerciallyemployed for metal to ceramic bonding purposes have generally consistedof lead, copper and titanium with or without small amounts of silver. Inthese alloys, the lead component has been employed as being the mosteffective ductile metal for lowering the melting point and increasingthe iiow of the alloy and its wetting effect.

The present invention is based on the discovery that certain alloyscontaining both lead and tin in addition to copper and titanium,introduced in the form of titanium hydride, unexpectedly provide jointswhich are substantially strong than those obtained by means of similarcopper, lead, titanium alloys free of tin. More specifically, it hasbeen found that marked improvements in bond strengths are obtained withfusible alloys consisting of from 45 to 70 parts by weight of copper, 25to 40 parts by weight of lead, 1 to 5 parts by weight of titaniumhydride and 2.5 to parts by weight of tin. A preferred alloy containsabout 58.5 parts copper, 31.5 parts lead, 2.5

parts titanium hydride and 7.5 parts tin. Titanium. may be substitutedfor all or part of the titanium hydride.

Features of the invention which are believed novel are set forth in theappended claims. The invention itself together with the variousadvantages thereof may be better understood from the followingdescription taken in connection with the accompanying drawing in which:7

FIGURE 1 is a sectional view of a metal-ceramic structure with theessential components thereof shown in their positions prior to formationof a joint between the metal and ceramic bodies; and

FIGURE 2 is a sectional view of the same component joined by the alloyof the present invention.

With reference to the accompanying drawing there is shown a ceramicbushing or insulator in the form of a disc 1 having an opening 2 thereinfor receiving an elec-. trically conducting metal pin 3.

For the purpose of making a strong hermetic joint bepresence of anon-oxidizing atmosphere such as hydrogen Patented June 16, 1964 "Ice 0opening 2. After cooling, there is obtained by means of the alloy of thepresent invention a joint between the ceramic member 1 and the pin 3possessing an unusually high bonding strength. V

Preferably the brazing ring 4 is made by compounding finely dividedlead, copper, tin, and titanium hydride with or without small amountsofbinders or lubricants such as parafiin or stearic acid which facilitatemolding of the mixture. The mixed powders are then compressedin dies toform rings of the desired size and shape. Following the above procedure,a number of metalceramic seals were producedemploying ceramic memberscomposed of: discs lot 96% alumina having a thickness of inch and holesof 2 or A; inch diameter. The terminal pins 3 were made from wire of 42%nickel-iron alloy orother suitable alloy cold-headed to form theshoulder 5. After cleaning these pins with hydrochloric acid solution,they were inserted into the holes 2 and with the brazing rings 4 inplace were fired at a temperature of 1800 F. in atmospheres of eitherhydrogen or diassociated ammonia for 10 to 12 minutes. The compositionsof the tested alloys including both those known prior to the presentinvention and those produced in accordance Table I.Braze CompositionsConstituents, Percent by Weight Braze No.

Cu Pb Tl Ag TlHz Sn Bronze 1 Oil-10% Sn.

tion was measured. A steady increased load was applied at a slow rateusing a tensile machine.

From the results of these tests as set forth in the above table, it-willbe seen that the joints formed with alloys containing no tin were ingeneral broken by the application of loads ranging from 450 to 850'pounds to the pin.

However as shown for example by, a comparisonof alloy' 20 containing notin with the alloys 23 to 28 inclusive con- I taining tin, thesubstitution of bronze for the copper thereby introducing tin into thealloy or the substitution of tin for a portion of the copper content ofthe previously known alloys, resulted in substantial increases in thestrength of the joints. cluded in the alloy, a force in excess of 1000pounds was required to produce failure. However as the application f ofthese additional loads, cause the pins to yield and upset to the extentthat they could not be pushed out, the

, results were tabulated as merely being greater than 1000 Inall caseswhere tin was in- 3 pounds. In these tests'in which the load exceeded1000 pounds, the ceramic members broke at loads ranging from 1050upwards to 2000 pounds.

The exact reasons for the improvements obtained by the presence of tinis not known. It is possible that the alloying of the tin with thecopper contents of the alloy may account for at least some of theimprovement obtained by the addition of tin. For example, braze #23containing 31.5% lead, 66% bronze in the form of a 90% copper-% tinalloy, and 2.5% titanium hydride appeared to produce the mosthomogeneous joint. Photomicrographs of this joint disclosed a bronzematrix surrounding islands of lead and a thin layer of titanium at theceramic surface. At the pin surface, there was an irregular layerresulting from the reaction between the alloy and the pin material.Sincetin is more expensive than lead or copper, it is desirable to limitthe tin content to a maximum of about 10%. In fact there appears to beno advantage in a tin content in excess of 10%.

While there has been shown and described particular embodiments of thepresent invention, it will be obvious to those skilled in the art thatchanges and modifications may be made therein without departing from theinvention and it is intended by the appended claims to cover all suchchanges and modifications as fall within the true spirit and scope ofthe invention.

What I claim as new and desire to secure by Letters Patent of the UnitedStates is:

1. A brazing material for bonding a metal member to a ceramic memberconsisting essentially of from 1 to 5 parts by weight of titaniumhydride, to parts copper, 2540 parts lead and 2.5 to 10 parts tin.

2. A brazing material for bonding a metal member to a ceramic memberconsisting of about 2.5 parts by weight of titanium hydride, 58.5 partscopper, 31.5 parts lead and about 7.5 parts tin.

3. A joint structure comprising a ceramic member and a metal memberjoined by a bonding material formed by fusing l-5 parts by Weight oftitanium hydride, 45 to 70 parts copper, 25-40 parts lead and 2.5 to 10parts tin.

4. A joint structure comprising a ceramic member and a metal memberjoined by an alloy formed by fusing 1-3 parts by weight of titaniumhydride, 45 to 70 parts copper, 2540 parts lead and 2.5 to 10 parts tinfused in an inert atmosphere.

References Cited in the'file of this patent v UNITED STATES. PATENTS2,351,798 Alexander June 30, 1944 2,570,248 Kelley Oct. 9, 19513,001,269 Moore Sept. 26, 1961

3. A JOINT STRUCTURE COMPRISING A CERAMIC MEMBER AND A METAL MEMBERJOINED BY A BONDING MATERIAL FORMED BY FUSING 1-5 PARTS BY WEIGHT OFTITANIUM HYDRIDE, 45 TO 70 PARTS COPPER, 25-40 PARTS LEAD AND 2.5 TO 10PARTS TIN.